SIAS sessional meeting: UK vaccination programme

Mr Dinani highlighted the ‘fascinating and frustrating’ search for statistics that the authors had undertaken in order to prepare the paper and the role of the UK Vaccination Programme Working Party.

Herd immunity and age at infection The presentation began with an introduction to the concept of herd immunity, whereby it is not necessary to immunise every member of the population to effectively eliminate a disease, but only a minimum threshold proportion. This threshold depends on the infectious strength of the disease. Reference was made to the topical issue of the MMR vaccine, which has only reached a national coverage level of 80% (dropping to 70% in some parts of London), while the coverage level required for the eradication of measles is over 90%. The impact of vaccination programmes on age at infection were considered using the example of an MMR vaccination programme in Greece. The programme had inadvertently changed the age profile of rubella infection in the population, particularly affecting women of childbearing age. This served as an example of the unforeseen consequences of a well-intentioned but poorly implemented vaccination programme.

Models and data The next section of the presentation dealt with two topics which are of particular interest to the actuarial profession models and data. An example was given of the modelling by Brisson et al of the Varicella Zoster Virus (VZV), which is responsible for both chickenpox and shingles. Exposure to chickenpox is thought to boost the immune response in later life to shingles. This leads to the interesting result that reducing exposure to chickenpox may well lead to a period of increasing incidence of shingles, which is a far more serious condition. A number of other models were also mentioned, before moving on to the difficulties of obtaining data. It is partly the result of the success of vaccination programmes in the past, that it is now a challenging task to find disease data that is both relevant to the current population of the UK and of a sufficient sample size to draw meaningful conclusions. Overall the authors were pleasantly surprised by the range and sophistication of the models which had already been developed and were in use, but were concerned about the paucity of data that were available to populate them.

Psychology in the risk-reward balance The third part of the presentation covered the psychology of vaccination decision-making, and striking the balance between risk and reward. The importance of the drivers behind parental decisions to vaccinate or not to vaccinate children is, of course, of relevance today with the ongoing MMR debate. Reference was also made to vaccination campaigns against polio, and the way in which the relative balance between the risk of the disease and the risk of the vaccine had changed dramatically from the 1950s to the present day.

Conclusion and discussion Wrapping up the presentation, the authors put forward the question of whether there was an opportunity for the actuarial profession and epidemiologists to share their skills in joint research projects. At this stage the chairman opened the discussion to the audience. Several speakers complimented the authors on their research and the paper itself, and went on to discuss vaccination programmes past and present around the world. As well as MMR, reference was made to SARS, rabies, malaria, and polio. The roles of actuaries in analysing statistical information and addressing the public perception of risk were also commented on. The opinion was expressed that actuarial answers were not always applicable to the real world and while the concept of herd immunity could be communicated to the general population, this could lead to a classic ‘prisoner’s dilemma’ the best course of action for the population at large may not be the best for the individual. SIAS was fortunate to have a guest present from the Health Protection Agency (HPA) who commented on several points raised in the discussion. She also outlined the work carried out by the HPA, including disease monitoring and the development of modelling techniques. Making reference to the role of stochastic models in the analysis of low-risk threats, she commented on the difficulty of the practical application of their results. She finished by highlighting the importance of risk communication to the public and the message that not vaccinating is an active decision in itself. The chairman then concluded the discussion and thanked the authors.